Gas discharge device



Sept. 28, 1931. H. GEFFCKEN ET AL 2,094,450

GAS DISCHARGE DEVICE Filed June 29, 1955 2 Sheets-Sheet 11 Q '1 14 Fig.5

1 17 i5 1 QINVENTOR 2U Human EEFFCKEN MAME RILHIEB 21 ATTORNEY Sept. 28,1937. E K Er AL GAS DISCHARGE DEVICE Filed June 29, 1935 2 Sheets-Sheet2 Fig.5

Patented Sept. 28, 1937 UNITED STATES.

acetate- PATENT cries GAS DISCHARGE DEVICE Application June 29,1933,Serial No. 678,127 In Germany July 23, 1932 16 Claims. (01.250-215) Our invention relates to electric discharge devices and moreparticularly to gaseous discharge tubes as used for amplification,rectification and generation of electric currents.

As is well known, gas discharge amplifiers differ from the known vacuumtube amplifiers by an increased discharge current due to the ionizationof the gaseous atmosphere preferably a noble gas contained in the tube.A further advantage of tubes of this type resides in the absence of ahot cathode liable to burn out after a limited number of operatinghours, thus making the life of gaseous discharge tubes practicallyunlimited.

In the usual construction, gaseous discharge tubes as used foramplification, rectification and similar purposes in the communicationand power engineering art, generally comprise a vessel filled with agaseous atmosphere preferably a noble gas and including a cathode and afirst anode or positive electrode hereinafter referred to as thedischarge anode. An electric glow discharge is set up between thecathode-and the discharge anode-serving as a source of negative ions andelectrons to be dissociated from the primary discharge and directedtoward a second positive or anode electrode, hereinafter called theoperating or suction anode. In a discharge tube of this kind, theprimary discharge between the cathode and the auxiliary or dischargeanode maybe likened to the hot cathode in a pure vacuum tube and servesas a source of pure negative discharge carriers (negative ions andelectrons) travelling to the operating or suction anode and capable ofbeing governed in a manner similar novel operation of and the provisionof means for gas discharge control devices for increasing thesensitivity and efficiency as compared to similar devices known in theart.

Further objects and aspects of our invention will become more apparentfrom the following detailed description taken in reference to theaccompanying drawings in which We have illustrated a few constructionsof discharge devices embodying the novel features of the invention.

Figure 1 shows schematically a simple form of electrode construction fora gaseous discharge device in accordance. with the invention.

Figure 2 shows an improved electrode structure according to theinvention.

Figures 3 and 4 represent characteristic curves explanatory of theoperation of gas discharge devices in accordance with the invention.

Figure 5 shows a circuit embodying a novel gas discharge device inaccordance with the invention for converting alternating current intohighly stable direct current.

Figure 6 illustrates another tube construction utilizing a heatedcathode in place of the cold cathode arrangement according to theprevious figures.

Figure 7 illustrates a discharge tube in accordance with the inventionespecially designed for amplifying purposes.

Figure 8 illustrates an operating characteristic curve of a tube asdescribed by Figure 7.

Figure 9 shows another design of a gaseous amplifying tube according tothe invention.

Figure 10 shows the discharge anode construction for atube of the typeshown by Figure 9.

Similar reference numerals denote similar parts throughout the differentviews of the drawings.

The novel features embodied in a. gaseous discharge tube in accordancewith the invention are based on the following considerations: Electronsemitted from a fiat shaped cathode ele c trode in a glow discharge tube,as is well known, leave the cathode surface substantially at rightanglesand retain this direction until they pass the region of the spacecharge filling the space parallel to the cathode surface. Only after theelectrons have'passed the space charge region, will the shape andconfiguration of the anode exert an appreciable influence upon thefurther movement of the electrons.

This fact is made use of in our invention as 40 illustrated by Figure lof the drawings showing a simple form of an electrode constructionembodying the invention. We have shown in Figure 1, a discharge vessell, preferably of fiattened shape filled with a gaseous atmosphere, suchas a noble gas, at reduced pressure and in cluding a cathode plate Zbentto the shape of a U, and a rectangular shaped anode 3 and a furtherauxiliary anode l of similar shape, both anodes being arranged in such amanner that their edges approximately coincide with the prolongation ofthe cathode surface 2. In a tube of this type, the electrons emittedfrom the cathode 2 travel along a path, as indicated by the dottedarrows, that is, at first at right angle to the cathode surface throughthe glowing layer 5 and then in a direction substantially parallel tothe cathode surface towards the anodes 3 and 4. By providing means in aknown manner to prevent further ionization along the path 53 such as bysuppressing a. positive column and an anode glow, a practically ion-freeelectron beam is obtained directed towards the anodes 3 and 4. We havediscovered that this electron beam is of well defined and concentratedshape and is capable of being easily and efiiciently controlled by meansof extremely small potential variations applied within a controllingregion (34) in the prolongation of the cathode surface. The edges of theelectrodes 3 and 4 enclosing the control region need not necessarilycoincide exactly with the prolongation of the cathode surface, butdeviations therefrom are admissible, especially when taking into accountthe effect of wall charges and of the cathode drop within the tube. Theelectrodes 2, 3, and 4 may be mounted and supported within the tube inany known manner and connected to the outside, such as by leads 2, 3,and 4' as shown.

We have discovered that especially favorable effects may be secured byusing a hollow cathode whereby a substantially increased cathode surfaceis obtained with a resultant increase of the emission current withoutincreasing the size of the other electrodes. By choosing a cathode ofcone shape or cylinder shape adapted to the shape of the dischargevessel, a uniform effect of the wall charge on the discharge is obtainedand unsymmetrical fields practically avoided, thereby materiallyincreasing the efficiency and performance of the tube.

A construction of this type is shown by Figure 2. We have shown adischarge tube I including a cup shaped cathode 6 and a pair of discshaped anodes l and 8 substantially conforming to the cross-section ofthe cathode and arranged at right angles thereto in a manner similar tothat described by Figure l. The first mentioned anode may be coveredwith an insulating coating 9, such as with a sheet of mica, covering theanode surface close to its edges. The surface of this insulator will benegatively charged during operation, thus exerting a repelling forceupon the electrons and serving together with the wall charges of thetube l to define and concentrate the tubular shaped discharge beamemitted from the cathode.

Referring to a practical example of a discharge tube according to theinvention, we have observed the following characteristics: By producinga primary discharge of about 50 milliamperes intensity between theelectrodes 6 (cathode) and 1 (discharge anode), and by plotting thevoltagecurrent characteristic for the second or operating anode 8 forpotentials in the vicinity of and taken relative to the potential of theanode characteristic discharge curves are obtained as shown by Figure 3,very much alike to the discharge characteristics of pure high-vacuumtubes known in the art.

For plotting these curves, a circuit may be used as shown by Figure 2comprising a suitable source of current, such as indicated by the plusand minus signs connected to potentiometer I0 provided with tapconnections for securing the potentials for the electrodes of the tube.The cathode 6 is connected to the negative terminal of source ID, thedischarge anode I is connected to a tap point on the potentiometer IE!supplying a positive operating potential, and the operating or suctionanode 8 is connected through an ammeter H to a variable contact on thepotentiometer to secure a varying potential in the vicinity of thepotential of the discharge anode 7.

We have furthermore shown a voltmeter 12 for indicating the potentialdifference between the discharge anode 1 and the operating anode 8.Curve a of Figure 3 was taken for a tube of the type according to Figure2 without the mica sheet applied to the discharge anode ll. It isreadily seen from this curve that the portion of the cathode rayemanating from the cathode and shooting past the anode is still capableof counteracting a negative bias of about 1 volt at 1.5 milliamperesintensity. With a two volt negative bias, the current becomes zero. Thiscurve represents an ideal detector characteristic having a very sharpbend and a. mutual conductance of more than 1.5 milliamperes per volt.

The curve b' has been plotted with the mica sheet 9 placed upon thedischarge anode i. It is readily seen from the shift of the bend towardsthe negative by an amount of almost 17 volts, that in this case themajor part of the electrons emitted from the cathode 6 travel past theanode l. The mutual conductance of the detector characteristic increasesto about 5 milliamperes per volt, and the relative emission yield withrespect to the available total emission current (50 milliamperes) isincreased.

We have discovered that the available mutual conductance may be furtherincreased by giving the electrode 8 the shape of a wire ring as shown,or of a narrow metal sheet cylinder (such as 42 in Fig. 9) in place of asolid or disc shape as shown in Figure 1; that is, in other words, byutilizing only the marginal zone for effecting control. In this lattercase, a slight increase of the negative bias of the electrodes willsuffice to deviate and return passing electrons towards the anode I. Byusing discharge tubes of this type and maintaining the proper operatingconditions, it was possible to secure mutual conductances of 14 to 20milliamperes per volt. This makes the tube admirably suited fordetecting purposes.

Tubes of this type represent practically ideal rectifiers, it beingpossible to shift the potential of the electrode 8 from the bend of thecharacteristic shown towards negative values by about 20 to 50 voltswithout increasing the ionic current flow over a few microamperes.

Essentially higher values of mutual conductance, however, with lessideal rectifying properties may be obtained by setting up the primaryglow discharge between the electrodes 6 (cathode) and 8 (dischargeanode); that is, by exchanging the connections for the electrodes 1 and8 in the circuit as shown by Figure 2. If now a current-voltagecharacteristic for the electrode 1 is plotted, a curve is obtained asshown by Figure 4 with no insulating or mica sheet applied to theelectrode 7. The mutual conductance will be nearly 5E! milliamperes pervolt. It is readily seen that a negative bias of the electrode 1 ofabout 1 volt relative to the anode 8 (position of the lower bend) issufficient to swell the tubular shaped cathode beam emitted from thecathode to such an extent that practically no electron reaches theelectrode l, whereas a potential shift of only 1 volt towards positivevalues will result in the flow of almost the. entire discharge current.

Discharge tubes according to the invention as described, may beadvantageously used as voltage stabilizers. In this case, it is possibleto secure a plurality of potentials by'arranging several operating orsuction anodes in spaced rela: tionship opposite the cathode B in placeof the single operating anode. 1 as shown in Figure 2. In this manner, avoltage stabilization'is obtained far superior to similararrangementsknown in the art.

We have furthermore discovered that tubes of the type according to theinvention may be used to great advantage for supplying highly stabilizeddirect current potentials from alternating current network's. We haveshown a circuit of this kind in Figure 5, comprising a gas dischargetube |3 including an anode l4 disposed intermediate a pair of cup shapedcathodes I5 and 15. We have furthermore shown two operating or suctionanodes l1 and I8 placed in the discharge path at either side of theanode l4. The alternating current is supplied through a transformer IS,the secondary of which has a center tap connected to the anode M. Theopen terminals of the secondary of the transformer I9 are connected tothe cathodes l5 and I6, as shown. It is possible under circumstances, todispense with the anode l4 since either cathode may alternately operateas an anode. The stabilized direct current potential is supplied fromthe terminals 2| connected between the center tap of the transformersecondary and the operating or suction electrodes l1 and [8. A singlecondenser 20 in parallel to the output terminals is sufficient to smoothout the alternating current ripples in View of the high stabilizingaction of the tube, thus making unnecessary the use of further smoothingelements, such as choke coils, et'c., and greatly simplifying therebythe circuit arrangements and decreasing costs.

The mutual conductance in the previous examples was given in relation tothe total glow discharge current. By increasing the primary glowdischarge current, the mutual conductance in general increasesproportionately. Such increase may be effected in a large degree bycoating the cathode with electron emitting material and heating it toemission temperature. In this case, the cathode is preferably made of atubular shape whereby the discharge takes place from the inside walls ofthe tube, thus avoiding any possible heat losses. In order to secure awell defined cathode beam, the cathode may be covered with a coveringmember having an opening to allow the escape of the electrons, or thecore containing the heating elements may be constructed in proper shapeto secure aconcentrated and well defined emission beam.

A practical embodiment of a cathode construction of this type is shownby Figure 6. The discharge vessel 22 contains the tubular shaped cathode23 which may be heated in a known manner by means of a heating elementincluded in a heater core 24. The open end of the cathode is covered bymeans of a plate 25 in sucha manner as to leave a narrow open margin.The plate 25 carries a collar 25. We have furthermore shown a heatscreen 21 extending beyond the opening of the cathode 23, thus leavingan annular open space between the collar 26 and the screen 21. In thismanner, a, directive action is exerted upon the cathode beam, insuring awell defined and highly concentrated discharge.

Anodes' 28 and 29 are arranged opposite the cathode in a manner similaras described in the previous figures. The operating voltage drop of atube of this type is about 15 to 25 volts, re-

sulting in an increased operating efliciency of tubesof this type ascompared with high vacuum tubes known in the art. 7 In order to startthe glow discharge or to-ignite the tube, a positive potential may beappli'edto the screen 21 for a short period, for which purpose thescreen 21 is carefully insulated from the other electrodes andprovidedwith "a separate-outside connecting lead sealed in the'tube. With tubesof this con struction, values of mutual conductance up to severalamperes per volt may be easily secured. It is understood that allfurther features regarding the direction and control of the cathode beamas described in previous and subsequent figures may be utilized in atube as described by Figure 6.

A noteworthy characteristic of the rectifying curves secured by means ofdischarge tubes according to the invention resides in their greatsimilarity with thermionic discharge characteristics obtained by meansof high vacuum tubes, as seen clearly from the diagrams according toFigures 3 and 4. From this it follows that the phenomenon is of purelyelectronic nature and that ionization has an appreciable influence onlyin the direct vicinity of the cathode electrode.

Starting from this recognition, we have endeavored to utilize thisphenomenon for designing a new and highly efficient amplifier. For thispurpose it is merely necessary, by means of suitably constructed andarranged auxiliary electrodes, tocontrol the number of those electronshitting the positive electrode serving as operating or suction anode. Amode of execution of a control tube of this type is shown by Figure '7.We have again shown a gas discharge vessel 30 including a cup shapedcathode 3|. The inside surface of the cathode and'the top outsidesurface are covered with mica sheets 3| to confine the glow dischargeproper to the cylindrical outside surface as shown at 5. The tubefurthermore contains two anode electrodes of similar shape and arrangedat right angles. to and spaced from the cathode, as described by theprevious figures. The primary discharge takes place between the cathode3| and the anode 33 (discharge anode) Whereas the anode 32 is used asthe operating or suction anode as shown by the connections to thepotentiometer I0 through the load circuit connected at 31. The operatinganode 32 is surrounded by a control electrode comprising two plates 34and 35 arranged at either side of the electrode 32. The input controlpotential is applied to' terminals 36 and the controlled or amplifiedcurrent is supplied from the output terminals-31. Tubes of this typeallow a control over a wide voltage swing and have a considerable mutualconductance. However, they are less suited for pure amplification onaccount of the appreciable currents inthe control (grid) circuit. Theymay-be used to great advantage for various other purposes, preferably:as regulating devices.

By exchanging theposition of the electrode 33 with the electrode system32, 34, 35, the possible voltage swing is somewhat decreased, on the onehand, but the grid currents, on the other hand, become inappreciablysmall. An operating characteristic secured from a tube of this type isshown by Figure 8. The voltage difference between the glow dischargeanode and the suction anode was about 4 volts. in the example,corresponding to this curve, the abscissae representing the input orgrid potential and the ordinates is. representing the output currents.With a primary discharge ofabout 50 milliamperes, the control currentswing is about 6 milliamperes. The characteristic has a typicallyparabolic shape so that the tube may be used advantageously forautomatic amplituderegulation. The maximum mutual conductance is about1.5 milliamperes per volt. i

In place of screening the suction anode by the control electrode-whichmay also have the shape of a grid in place of a solid electrode asshown-we have found it advantageous to arrange the grid in such a mannerthat the electron beam is controlled by deviation by the grid towardstheoperating or suction anode. In this manner, the grid currentsdecrease with increasing anode current, a condition of great importancefor the design of amplifying apparatus.

A tube of this type is shown by Figure 9 of the drawings. The dischargevessel 38 includes a tubular cathode 39 of similar construction asdescribed by Figure 7, a discharge anode 40 covered with a mica sheet4!, a cylindrical suction anode 42 and a control electrode 63 consistingof a plurality of wire rings. The discharge anode 4D is provided'withcut-out openings 44, as shown by Figure 10, separated merely by narrowstiffening portions. The tubular shaped electron beam emitted from thecathode 39 passes through the holes 44 into the space enclosed betweenthe suctionanode 42 and the control electrode 43. The suction anode'42and the control electrode (grid) 43; are preferably biased negatively bya few volts relative to the discharge anode ill. The number of electronsattracted by the suction anode will be the higher, the higher thenegative bias of the control electrode 43.

The amplifying tubes above described may obviously be provided with aheated cathode in place of the cold glow discharge as shown and since itis well known that considerably increased emission currents are obtainedwhen using an attenuated atmosphere due tothe influence on the spacecharge as compared with a high vacuum, amplifying tubes are obtained inthis manner of appreciable performance and efliciency as compared tosimilar devices known in the prior art.

The filling to be used for discharge tubes according to .the inventionpreferably consists of gases being free from metastable conditions, suchas argon and crypton. A special advantage of the noble gases resides intheir high ionization potential and it is therefore preferable to usegases in as pure a state as possible. The gaseous pressure should be lowto avoid a disturbing dispersion of'the cathode beam, and we have foundit advantageous to use pressures below 5 millimeters Hg. When using coldcathodes the most favorable operating region, depending on the gas usedand on the cathode material used is about 5 to-.2 millimeters Hg. Whenusing hot cathodes,

the pressure may be considerably decreased, in

some cases below one-thousandth of a. milli meter. In this case, it hasbeen found favorable to usemercury vapor or the heavy noble gases, suchas xenon and crypton, on account of their high compensating effect onthe space charge in the tube.

The constructions shown in the drawings are specially characterized bythe feature that the anodes are formed geometrically similar to thecross-section of the cathode and arranged concentrically'in the tube insuch a manner, that their edge-zones approximately coincide with theprolongation of the cathode surface. By these means betweenthe-preferably metallizede. g.

silveredinner walls of said tube and the cathode surface a tubularshaped stream of electrons is formed which is directed to the edge-zoneof the discharge anode and which by very low controlling potentials maybe swelled or chocked thus passing or reaching the operating anode.

Although we have described our invention specifically with reference tothe constructions and embodiments shown by the drawings, it isunderstood that the broad ideas and underlying principles of theinvention are subject to numerous variations and modifications comingwithin the broad scope and spirit of the invention as eX- pressed by theensuing claims.

We claim:

1.- A glow discharge device comprising a tubular shaped vessel filledwith a gaseous atmosphere at reduced pressure, a hollow cylindricalcathode arrangedncoaxially to and within said vessel and having itsinner surface lined with insulating material, a first disc shaped anodesubstantially equal to the cross-section of said cathode and disposedcoaxially and in spaced relationship thereto for producing aconcentrated annular electron discharge stream from the outer surface ofsaid cathode to said anode and a second electrode of similar shape tosaid anode arranged in spaced relationship and coaxial with said anode.

2. A glow discharge device as claimed in claim 1 in which said dischargeanode is closest to the cathode and is covered with an insulatingcoating close to its edges.

3. A glow discharge device as claimed in claim 1 including a controlelementfor influencing the discharge current to said operating anode.

l. A negative glow discharge device comprising a tubular shaped vesselfilled with a gaseous atmosphere at reduced pressure, a hollowcylindrical cathode arranged coaxially with and within said vesselhaving its inner surface lined with insulating material, a first discshaped anode arranged coaxially with and in spaced relationship to saidcathode, means for setting up an electric glow discharge between saidcathode and said anode, and a second annular shaped operating anodespaced from and disposed coaxially to said first anode.

5. A glow discharge device as claimed in claim 4 including a controlelectrode for influencing the discharge current to said second anode.

6. A glow discharge device as claimed in claim 4 in which said firstanode is arranged closest to said cathode and provided with openings toallow the passage of the discharge stream to said second anode.

7. A glow discharge device comprising a tubular shaped vessel filledwith a gaseous atmosphere at reduced pressure, a cup-shaped cylindricalcathode electrode mounted coaxially with and within said vessel, a discshaped discharge anode electrode arranged in spaced relationship to theopen end of and coaxially with said cathode, a second operating anodedisposed in spaced relationship to said discharge anode and away fromsaid cathode, means including a coating of insulating material coveringthe inner walls and the outer bottom wall 'of said cathode cup forsetting up a negative glow discharge between the outer cylindricalsurface of said cathode and said discharge anode to produce a tubularshaped stream of negative discharge carriers substantially parallel tothe cylindrical surface of said cathode and in a direction towards saidoperating anode, said first anode being provided with openings forpassing said negative discharge stream.

8. A glow discharge device as claimed in claim '7 in which the surfaceof said discharge anode facing said cathode is covered with a coating ofinsulating material.

9. A glow discharge device as claimed in claim '7 including a controlelectrode arranged to control the discharge stream to said operatinganode.

10. In a glow discharge device as claimed in claim '7 in which saidoperating anode is of cylindrical ring-shape and disposed coaxially tosaid discharge anode and a cylindrical control grid electrode arrangedcoaxially with and surrounding said operating anode.

11. An electrical discharge device comprising an envelope, a gaseousatmosphere therein, a cylindrical cathode, a disc-shaped anode ofsubstantially equal contour to the cross-section of said cathode andarranged coaxially with said cathode and spaced therefrom, meansincludin a member disposed adjacent to the inner surface of the cathodeto produce an annular electron discharge stream from the outer surfaceof said cathode to said anode, and a further anode electrode spaced inrelation and coaxial to said first anode and adapted to variablyconcentrate and diffuse said electron stream.

12. An electrical discharge device comprising an envelope, a gaseousatmosphere therein, a cylindrical cathode, a disc-shaped anode having adiameter substantially equal to the diameter of said cathode andarranged coaxially with said cathode and spaced therefrom, meansincluding a member disposed adjacent to the inner surface of the cathodefor producing an annular discharge stream between the outer surface ofsaid cathode and said anode, and further electrode means for varying thedegree of concentration of said stream in accordance with inputpotential fluctuation.

13. An electrical discharge device comprising an envelope, a gaseousatmosphere therein, a cylindrical cathode therein having an outerelectron emitting surface, a disc-shaped anode of substantially equalcontour to the cross section of said cathode and arranged in spacedrelation to and coaxially with said cathode for producing a concentratedannular electron discharge'stream between said emitting surface and saidanode, and an additional electrode of substantially equal contours toand arranged coaxially with said anode and adapted to vary the degree ofconcentration of said electron stream in accordance with appliedcontrolling potential variations.

14. A gas discharge tube for the amplification, rectification, orgeneration of electric current fluctuations comprising a vessel, agaseous atmosphere therein, a cylindrical cathode therein having anouter emitting surface, a layer of insulating material disposed adjacentto the inner cathode surface, a first anode being disposed at rightangle to the axis of said cathode and havin its contour substantiallyequal to and'in line with the prolongation of the cathode cylindersurface, means for setting up a substantial annular shaped gas dischargestream from the outer surface of said cathode to said anode, and atleast one further electrode spaced from said anode for attractingelectrons from said discharge stream around the edge of said firstanode.

15. An electrical discharge device comprising an envelope containing agaseous medium, a cylindrical cathode having an electron emittingsurface, a similarly shaped member spaced from and enveloping saidcathode and adapted to have a suitable potential impressed thereon, adiscshaped anodeof substantially equal contour to the cross section ofsaid cathode and arranged in spaced relation to and coaxially with saidcathode for producing a concentrated annular electron discharge streambetween said emitting surface and said anode, and an additionalelectrode of substantially equal contour to and arranged coaxially withsaid anode and adapted to vary the degree of concentration of saidelectron stream in accordance with applied controlling potentialVariations.

16. An electrical discharge device comprising an envelope containing agaseous medium, a cathode having an extended emitting surface, means forconcentrating the electron emission from said cathode into an annulardischarge beam, an anode of substantially equal contour to the innercross-section of said discharge beam and arranged in spaced relation tosaid cathode and coaxially within said beam, and an additional electrodeof substantially equal contour to and arranged coaxially with said anodeand adapted to vary the degree of concentration of said electron beam inaccordance with applied controlling potential variations.

' HEINRICH GEFFCKEN.

HANS RICHTER.

